An 83(b) election lets a founder or employee pay ordinary income tax on restricted stock at its value on the day it's granted, rather than as it vests, locking in a usually much lower tax basis while the stock is still worth close to nothing.
Without the election, tax is owed on the value of each tranche as it vests, which can mean a large, unplanned tax bill years later if the company's value has grown significantly by then. Filing early, while the stock's fair market value is at its lowest, trades that risk for a small, known cost paid upfront.
The catch is the deadline. The IRC §83(b) filing deadline is a hard 30-day cutoff from the grant date, no extensions, no exceptions for missing it by even a day. It's one of the few tax elections where being a week late doesn't mean a penalty; it means the election simply doesn't exist anymore for that grant.
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